Add CSS to Vue using JavaScript

I am trying to add style to this <label> tag on Vue.

  <div class="grid grid-cols-1 mt-5 mx-7">
      <label class="uppercase md:text-sm text-xs text-gray-500 text-light font-semibold mb-1 flex items-center justify-center">Upload Photo</label>
        <div class='flex items-center justify-center w-full'>    
            <label  id="img1" class='flex flex-col border-4 border-dashed w-40 h-32 hover:bg-gray-100 hover:border-purple-300 group'>
                 <div @click="onPrimaryPicSelected" class='flex flex-col items-center justify-center pt-7'>
                  <svg class="w-10 h-10 text-purple-400 group-hover:text-purple-600" fill="none" stroke="currentColor" viewBox="0 0 24 24" xmlns="http://www.w3.org/2000/svg"><path stroke-linecap="round" stroke-linejoin="round" stroke-width="2" d="M4 16l4.586-4.586a2 2 0 012.828 0L16 16m-2-2l1.586-1.586a2 2 0 012.828 0L20 14m-6-6h.01M6 20h12a2 2 0 002-2V6a2 2 0 00-2-2H6a2 2 0 00-2 2v12a2 2 0 002 2z"></path></svg>
                  <p class='lowercase text-sm text-gray-400 group-hover:text-purple-600 pt-1 tracking-wider'>Select a photo</p>
                </div>
              <input type='file' class="hidden" />
            </label>
        </div>
    </div>

I want that when the onPrimaryPicSelected function is called to add a CSS styling to the <label> tag. How can I do this if it is possible?

Currently the onPrimaryPIcSelected just gets the image that was uploaded.

 onPrimaryPicSelected(event) {
      this.primaryPhoto = event.target.files[0];
      this.primaryPhotoUrl = URL.createObjectURL(event.target.files[0]);
    },

Answer

You can use a boolean variable if true it will apply your style to the label tag.

<div class="grid grid-cols-1 mt-5 mx-7">
  <label class="uppercase md:text-sm text-xs text-gray-500 text-light font-semibold mb-1 flex items-center justify-center" :style="selected ? 'your-style-here' : ''">Upload Photo</label>
    <div class='flex items-center justify-center w-full'>    
        <label  id="img1" class='flex flex-col border-4 border-dashed w-40 h-32 hover:bg-gray-100 hover:border-purple-300 group'>
             <div @click="onPrimaryPicSelected" class='flex flex-col items-center justify-center pt-7'>
              <svg class="w-10 h-10 text-purple-400 group-hover:text-purple-600" fill="none" stroke="currentColor" viewBox="0 0 24 24" xmlns="http://www.w3.org/2000/svg"><path stroke-linecap="round" stroke-linejoin="round" stroke-width="2" d="M4 16l4.586-4.586a2 2 0 012.828 0L16 16m-2-2l1.586-1.586a2 2 0 012.828 0L20 14m-6-6h.01M6 20h12a2 2 0 002-2V6a2 2 0 00-2-2H6a2 2 0 00-2 2v12a2 2 0 002 2z"></path></svg>
              <p class='lowercase text-sm text-gray-400 group-hover:text-purple-600 pt-1 tracking-wider'>Select a photo</p>
            </div>
          <input type='file' class="hidden" />
        </label>
    </div>
</div>

then in your function

onPrimaryPicSelected(event) {
  this.selected = true;
  this.primaryPhoto = event.target.files[0];
  this.primaryPhotoUrl = URL.createObjectURL(event.target.files[0]);
},