style.css

 html,
 body {
   margin: 0;
   padding: 0;
   height: 100%;
 }

 /* Stlying Variabes for Light Theme */
 .theme-light {
   --color-primary: #0060df;
   --color-secondary: #fbfbfe;
   --color-accent: #fd6f53;
   --font-color-one: #000000;
   --font-color-two: #000000;
 }

 /* Styling Variables for Dark Theme */
 .theme-dark {
   --color-primary: #17ed90;
   --color-secondary: #243133;
   --color-accent: #12cdea;
   --font-color-one: #ffffff;
   --font-color-two: #ffffff;
 }

 /* More Custom Theme classes stlying can be added here */

 .container {
   display: flex;
   width: 100%;
   height: 100%;
   background-color: var(--color-secondary);
   flex-direction: column;
   justify-content: center;
   align-items: center;
 }

 .container h2 {
   color: var(--font-color-one);
 }

 .container button {
   position: absolute;
   left: 10px;
   top: 20px;
   color: var(--font-color-one);
   background-color: var(--color-primary);
   padding: 10px 20px;
   border: 0;
   border-radius: 5px;
 }